As is well known, fan-cooled refrigerators have a damper provided on the outlet of an air supply duct through which cold air generated by an evaporator is supplied to a compartment. The damper opens and closes the outlet in order to control the interior temperature of the compartment. This conventional damper is provided with a motor for driving a damper blade and a position detection switch whose contacts are opened and closed in accordance with the position of the damper blade. The damper is controlled to open and close the outlet in accordance with the compartment's interior temperature, which is detected by a temperature sensor provided therein, and in accordance with the detected position of the damper blade, so that the compartment's interior temperature is maintained at a set temperature.
If, however, the damper is subject to frosting, the damper will not open and close the outlet of the air supply duct even when the motor is operated, and the temperature within the compartment will vary from a set temperature. In other words, when the damper is frosted and locked in the closed position, there will be an abnormally high temperature within the compartment. When the damper is frosted and locked in the open position, there will be an abnormally low temperature within the compartment.
In order to solve this problem, the inventor has previously provided a refrigerator with a heater in order to defrost the damper. An example of such a refrigerator is disclosed in Japanese Utility Model Laid-Open Publication No. 62-93676, filed on Nov. 30, 1985. In Japanese Utility Model Laid-Open Publication No. 62-93676, the damper on the outlet of the air supply duct is provided with a heater, in addition to the motor and the position detection switch. Also, a timer is provided in a control circuit which controls the operation of the motor to open and close the damper properly. The timer counts the period for which an operating signal to drive the motor is being generated from the control circuit, and when the timer counts up a prescribed value without being reset by receiving a proper position detecting signal generated from the position detection switch, the heater is energized until the damper has been defrosted and the proper position detecting signal is generated.
In the above described device, however, it is not possible to distinguish between a damper malfunction caused by failure of the motor, the position detection switch, or damper elements, such faulty pin or a leaf spring, and the case where the damper has frosted, because the malfunction of the damper is detected by the timer. Therefore, when the malfunction of the damper is caused by something other than frosting, the malfunction will not be corrected even though the heater is energized, and the energizing of the heater will continue in an uncontrolled fashion, leading to wasteful power consumption. Particularly if the damper is locked in the closed position, the rising of temperature within the compartment is further enhanced.